Greetings this is karlsen i am very happy that you go and check this thread.
First of all you need:
1: A computer that is able to run 3 or more clients of wow and is able to load farst.
2: A high level that can boost your alt.
3: A alt that can be boosted by your high level char.
4: Being able to make a trial account
5: Active server
1: When you wanna start doing this you need someone from another account to invite your high level, your alt and your trial account char. This can be done by asking a random guy at level 16. When this is done ask him to give your trial account char the lead.
2: Kick the one that invited you and thank him for helping you out.
Turn the loot to free for all on the trial account.
Go log your main and go to the instance you wanna boost your alt in.
Make sure mobs at entrance won't attack the alt.
3: Now log alt with another client of wow than your main, go to instance and stand at entrance.
4: Log your main and pull the mobs to where you left your alt.
5: Now FAST! log your alt. imedently when you see you're logged in tab over to the mains client of wow and log in.
6: AOE or just kill mobs slowly (when alts goes offline in chat STOP Killing or it won't get xp)
7: When that is done you can relax and log your alt and enjoy loots.
8: When everything you want/need is looted go to a new safe spot in instance that is longer inside the instance.
9: Log main and pull, to the alts safe spot. And log alt with alt client of wow.
10: log main fast after you have logged alt and now aoe/kill mobs.
11: log alt when everything that was pulled is dead, and enjoy loot.
12: Repeat step 8-11
I have tried this patch 3.0.3 and worked fine.
Theory:
You gain xp on your char as long as you're online and in the group.
That was all, if i had said something that sounds stupid please tell me and please move your trial account every 29 min or it will be ruined. The trial account can be replaced with friend but imo trial account is better way.
Last but not least: I have chosen to make this in exploit forum since i am pretty sure it is not supposed to be this way.
Tbh you only use 1 payed account for this trick/exploit.